Novel process and product

ABSTRACT

This invention relates to novel compositions and to a process of preparing an iridescent chromium plated article which comprises passing current from an anode to a cathode through an aqueous chromium plating solution which contains at least one chromium compound providing chromium metal ions for electroplating chromium and a hexavalent molybdenum compound to produce an iridescent chromium surface on said cathodic article.

United States Patent Chessin et al.

[151 3,657,079 1451 Apr. 18, 1972 I54] NOVEL PROCESS AND PRODUCT [72] Inventors: Hyman Chessin, Birmingham; Robert Francis Gempel, Detroit, both of Mich.

'52 us. 0 I. ...204/51, 204/41, 204/43 51 Int. Cl. ..C23b 5/06 [58] Field 6: Search ..204/43, 51; 148/616, 6.17

[56] References Cited UNITED STATES PATENTS 1,795,459 3/1931 Westbrook .204/51 2,516,227 7/1950 Ma .204/43 FOREIGN PATENTS OR APPLICATIONS 617,292 2/1949 Great Britain .204/51 OTHER PUBLICATIONS B. A. Shenoi et al., Metal Finishing, Vol. 63, pp. 56- 59, May 1965 and pp. 94- 97, June 1965. Chemical Abstracts, Vol. 70, p. 504, 4343 Id, 1969 Primary Examiner-G. L. Kaplan Attorney-Lewis C. Brown, Kenneth G. Wheeless and Robert P. Grindle [5 7] ABSTRACT This invention relates to novel compositions and to a process of preparing an iridescent chromium plated article which comprises passing current from an anode to a cathode through an aqueous chromium plating solution which contains at least one chromium compound providing chromium metal ions for electroplating chromium and a hexavalent molybdenum compound to produce an iridescent chromium surface on said cathodic article.

4 Claims, No Drawings This invention relates to a novel decorative metal coating, to bath compositions used to prepare such coatings, and to processes for the preparation of such metal coatings. More particularly, this invention relates to decorative electrodeposited chromium surfaces which have iridescent properties.

According to one aspect of the invention, a bath containing a hexavalent chromium compound and a hexavalent molybdenum compound is employed to produce an electroplated article with a chromium metal surface which reflects light to give an iridescent, rainbow effect.

The aqueous chromium plating solution employed according to the invention may be prepared from commercial chromic acid solutions. Preferably, a portion of the chromic acid used in the bath composition may be replaced by a salt of hexavalent chromium such as sodium chromate, sodium dichromate, potassium chromate, potassium dichromate, strontium chromate, magnesium dichromate, lanthanum chromate, lanthanum dichromate, etc. In many cases it may be advantageous to employ one or more of such salts in order to provide for a means of control of the composition or of the acidity of the aqueous chromium plating bath.

Any molybdenum compound soluble in the bath composition which yields hexavalent molybdenum may be employed as a component of the aqueous chromium plating bath composition to provide a chromium plated article having iridescent properties. Molybdic acid is a highly preferred component which may be employed in the bath composition. Typically, molybdic acid may be used as an ammonium complex of molybdic oxide containing about 8.5 percent by weight of ammonium ion and about 85 percent by weight molybdic oxide. Other typical hexavalent molybdenum compounds which may be used include sodium molybdate, phosphomolybdic acid, etc.

Catalyst anions may also be included in the aqueous chromium plating bath to regulate the concentrations of the active ingredients during electroplating. For example, sulfate, fluoride, and complex fluorides may be used. Typically, fluosilicates, fluoborates, fluoaluminates, fluotitanates, and fluozirconates may be included in the aqueous chromium plating bath composition without adversely affecting the iridescent light reflective properties of the novel decorative chromium electroplate which is produced according to the invention.

Suitable neutralizers and/or buffers may also be employed in the bath composition of the invention. Examples of such neutralizers or buffers may include phosphates, borates, sulfonates, and carboxylates. In addition, catalyst anions as heretofore recited may also be used in amounts sufficient to act as buffers or neutralizers in combined effect with their catalyst properties.

A typical bath composition which may be used according to the process of the invention to produce an iridescent chromium electrodeposit may comprise chromic acid in an amount of 50 600 g/l as CrO in combination with a hexavalent molybdenum compound in an amount of 2 140 g/l as M00 Other adjuvant materials may be included in the bath.

A specific bath composition may contain the following ingredients in the amounts indicated:

chromic acid 300 g/l sulfate l.2 g/l molybdic acid (85% by weight) llO g/l concentrated ammonium hydroxide 20 mil TABLE I silicofluoride 0.5-5.0 gll phosphate 0.35-3.5 g/l acetate 2.0-20 g/l The catalyst and/or buffer anions may be employed individually or in any combination wherein the combined amounts of said catalyst anions may be 0.3 30 g/l based upon the weight of the total bath composition.

Other typical materials which yield regulating buffer ions include trichloroacetic acid, succinic anhydride, adipic acid, and sodium aluminate. Said ingredients may be used in the iridescent chromium plating bath compositions of the invention in amounts (based upon the total weight of the composition) of 0 40 g/l.

In an iridescent chromium plating bath employed according to the invention, the ratio of chromic acid (CrO to (calculated) molybdenum trioxide (M00 may be from 3:1 40:1. Thus, for an aqueous iridescent chromium plating bath which may contain 250 g/l chromic acid (CrO the bath composition may contain 40 70 g/l of molybdic acid (M00 Amounts of chromic acid as CrO of from 50 600 g/l may be used and, preferably, baths containing 225 275 g/l of chromium and 30 g/l of molybdic acid as M00 are employed.

The iridescent chromium plated articles prepared using the compositions of the invention may contain mounds of chromium deposits having a mean height above the surface of 0.025 5 microns wherein said mounds are positioned in adjacent and semi-overlapping strings, said strings being positioned in approximately parallel configurations to form an iridescent chromium surface having about 70 1,500 strings per millimeter and 6 X 10 6 X 10 mounds of chromium deposits per square centimeter of surface. Such iridescent chromium plated articles may be subsequently given a supplementary metallic coating of metals such as nickel, copper, chromium, etc. to enchance or modify the color or reflectivity of the iridescent surface. Similarly, organic or inorganic coatings may be used to vary the decorative rainbow effects on all or a portion of said surfaces.

The mounds of chromium deposits are roughly circular in cross section and may have a curvature approaching that of a sphere or a portion of a sphere. The mean height of a mound of chromium deposit is measured from the plane which joins the totality of points representing the average of the minimum and maximum of the surface upon which said mounds are positioned. Microscopic examination of said surface shows that the mounds of deposit may be completely separate with distances between said mounds of up to three or four mound diameters. The mounds may touch or overlap to form continuous strings or semi-continuous strings, said strings being positioned in approximately parallel configurations analogous to strings of beads placed upon and conforming the shape of a given surface. It is believed that the parallel configurations (which are not necessarily linear) produce an effect such as may be obtained from a diffraction grating using parallel lines. It has been found that particularly striking iridescent effects may be obtained from an iridescent chromium plated article wherein the article contains about 6 X 10 6 X 10 mounds having an average height of 0.025 5 microns, wherein the mounds are positioned on the surface of said iridescent chromium plated article so that a series of continuous lines connecting the centers of said mounds produces a network of lines and said network of lines contains at least 790 parallel lines per linear centimeter of length as measured by intersecting points on a straight line drawn in any direction for a length of I centimeter from the center of a given mound of iridescent chromium plated surface. Thus, a line of l centimeter length drawn from any given mound on the chromium plated surface of the iridescent chromium plated article of the invention intersects at least about 790 approximately parallel strings of mounds when such strings of mounds are connected by lines drawn to the centers of the mounds comprising said approxi mately parallel strings.

Bright iridescent chromium plated articles may be characterized as having a surface containing mounds of chromium deposits wherein the average height of the mounds is about 0.075 2.5 microns and wherein the average space between faces were obtained using a plating time of 1 minute to produce the chromium electrodeposits.

EXAMPL 3 any two approximately parallel ad acent strings of mounds (as 5 E measured by the average distance between the two lines join- An iridescent chromium plating bath composition was ing the center of each of the mounds of each string) is about prepared by combining the following ingredients in the in- 2.5 microns. Particularly brilliant iridescent chromium plated dlcated concentrations watel'i surfaces may be obtained when the average height of the mounds is about 0.087 microns and the average space V Grams per litcr(g/l) between any two approximately parallel adjacent strings of fillzg' l 'ygg 28 mounds (as measured by the average distance between two Sum: (50?) 3 L2 lines joining the center of the mounds of each string) is ap- Fluoride 5- 0.4 proximately 2.9 3.0 microns. Phosphate (PO4 0.6 The following examples are submitted for the purpose of illustration only and are not to be construed as limiting the A die-cast automobile door handle was connected as elecscope of the invention in any way.

trode and immersed in the above iridescent chromium electroplating composition. Electroplating current was passed through the article to be electroplated and the solution at a temperature of about 44 C to obtain an iridescent chromium EXAMPLE 1 electroplate on the die-cast automobile door handle. An iridescent chromium plating bath composition was prepared by combining the following ingredients in water with EXAMPLE 4 the indicated concentrations (all concentrations being in An iridescent chromium plating bath composition was grams per liter of total solution unless otherwise specified herein). prepared by combining the following ingredients in the in- I dicated concentrations in water:

Grams per liter (g/l) Chromic Acid (CrO 250 Molybdic acid (85%) 50 Grams per liter (g/l) Fluoride (P) 03 Chrome Acid (CrO,) 250 shihiie ($0 1.0 S i 0 u a e 2555515 '3": p i Phosphate (Po,---) 0.4

Acetate (CA-k0,) l4 A steel strip was chromium plated in the above iridescent chromium plating solution by passing plating current through A copper plated strip was connected as electrode, immersed said bath composition using the metal strip as electrode for 5 40 in the above iridescent chromium plating composition and minutes at a temperature of 4045 C. The chromium plated current was passed through said solution at about 44 C to article was removed from the bath, rinsed, dried, and was produce a lrldescent chromium electrodeposit on said noted to display an iridescent effect when exposed to sunlight copper p- I and tifi i l m The following Examples 5 20 were carried out in a Hull 45 Cell in order to demonstrate that iridescent chromium EXAMPLE 2 deposits may be produced according to the process of the in- E l l t d a ickel late d Steel Sm as vention over wide current density ranges. The concentrations I A g e 3 n l b h (in grams per liter unless specified otherwise) are given for e ectro 6 mt e m escemc romlumop i at c9mp?smon each ingredient in the aqueous iridescent chromium plating of Exfample 1 at a temperature of 49 a P]an ng of 50 bath and the results and conditions are summarized in Table 15 minutes and a plating current density of approximately 20 In each Example 3 Standard plating time of 5 minutes was asd (amperes per square decimeter). The chromium plated arused and the temperature was maintained at 43 44 C f ticle obtained was noted to produce iridescent effects when purposes f comparison h total length f the Standard Hull exposed to sunlight and artificial light. Similar iridescent sur- C ll d i the e i e t w 100 illi ete TABLE 11 Standard Length of Ingredient concentration (g./l.) I'Iull cell Hull cell current iridescent CrO; M005 S04 P04 CQHJOZ Othcr (amps) span (mm.) Remarks 500 140 2.5 0 0 N320 g./l.) 12 53 Excellent. 400 119 2.0 0 0 NazO 51 g./l.) 12 45 D0. 250 42.5 0.0 0.7 15.6 F- (0.3 g./l.) s 60 Superior. 128 21.3 0.46 0. 36 0.7 ZrFh- (0.31 g./l. s 56 D0. 80 8.5 0. 29 0. 22 10.6 F- 0.10 g./l. s 53 DO. 300 50 0 0.42 18 siFe- (6.0 g./l.) s 68 Do. 300 60 1.2 0 0 01100 40-55 g s 50 Excellent 250 50 0.9 0.7 15.6 F- (0.3 g./l.) 8 Superior. 200 45 0.8 0 0 NazO (7.6 g./ 8 62 Excellent. 300 60 1.1 +0.7 0 s 45 DO. 250 42.5 0.9 0.7 15.6 SlFa' (0.9 g./l.) 8 60 Superior. 250 42. 5 0. 0 0.7 15.6 TiFn' (0.75 g./l.) 8 02 Do. 250 42.5 0.0 0.7 15.0 ZrFB- (0.6 g./l.) s 61 250 42.5 0.6 0.7 15.0 AlFs 1.2 g./l.) s 50 D0. 250 0 0. 6 0. 7 1 .6 SIFB' (0.9 sen/l.) 8 0 }Ordinary chromium plate 250 0 1.0 0.4 14.6 F (0.3 g./l.) I2 0 no iridescent cllects.

As can readily be seen from Table II excellent or superior results were obtained using the compositions set forth in Examples 5 18, whereas an ordinary chromium plate was obtained in Examples 19 and 20 (denoted as standards) when hexavalent molybdenum was omitted from the bath compositions. In Table II a Hull Cell containing an iridescent span of at 1 least 40 millimeters of continuous length of the Hull Cell is considered to have an excellent rating, whereas continuous iridescent spans of over 55 millimeters in length are considered superior. In each case the iridescent effect was compared both in natural sunlight and in artificial light including incandescent and fluorescent light.

Although this invention has been illustrated by reference to specific embodiments, modifications thereof which are clearly within the scope of the invention will be apparent to those skilled-in-the-art.

We claim:

1. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium which contains 50 600 g/l CrO as chromic acid and 2 140 g/l of M00 as molybdic acid, 0.3 to 3.0 grams per liter of sulfate anions, 0.1 to 1.0

grams per liter of fluoride anions, 0.35 to 3.5 grams per liter of phosphate anions, and 2.0 to 20 grams per liter of acetate anions.

2. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium as claimed in claim 1 wherein the chromium plating bath composition contains at least one anion selected from the group consisting of fluosilicates, fluoborates, fluoaluminates, fluotitanates, and fluozirconates.

3. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium as claimed in claim 1 wherein the chromium plating bath composition contains up to about 30 g/l of at least one anion selected from the group consisting of fluosilicates, fluoborates, fluoaluminates, fluotitanates, and fluozirconates.

4. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium which comprises 225 275 g/l CrO as chromic acid, 30 g/l M00;, as molybdic acid, 0.7 1.2 g/l sulfate ion, 0.2 0.9 g/l fluoride ion, 0.5 1.2 g/l phosphate ion, and 12 19 g/l acetate ion. 

2. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium as claimed in claim 1 wherein the chromium plating bath composition contains at least one anion selected from the group consisting of fluosilicates, fluoborates, fluoaluminates, fluotitanates, and flUozirconates.
 3. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium as claimed in claim 1 wherein the chromium plating bath composition contains up to about 30 g/l of at least one anion selected from the group consisting of fluosilicates, fluoborates, fluoaluminates, fluotitanates, and fluozirconates.
 4. An aqueous chromium plating bath composition for electrodeposition of iridescent chromium which comprises 225 -275 g/l CrO3 as chromic acid, 30 - 80 g/l MoO3 as molybdic acid, 0.7 - 1.2 g/l sulfate ion, 0.2 - 0.9 g/l fluoride ion, 0.5 - 1.2 g/l phosphate ion, and 12 - 19 g/l acetate ion. 